Vegetation–environment relationships in irrigation channel systems of southern Argentina

Abstract

Using a multivariate approach, relationships were determined between functionally defined groups of aquatic plants and the disturbance and stress pressures associated with ambient conditions and management regime in artificial channel systems of two irrigation districts located in the lower valleys of the Rı́o Colorado and Rı́o Negro, Argentina. Canonical Correspondence Analysis (CCA) of 1993–1994 survey data showed that the distribution and abundance of aquatic vegetation was closely related to water conductivity, winter drought, water depth, water movement and management regime. Indices of disturbance and stress were constructed from combined environmental data for each site. CCA showed that each variable (disturbance or stress) explained about half of the constrained variation. Four functional plant groups were identified using cluster analyses, occurring in different sets of disturbance and stress conditions. Two groups (including Charophyta, Potamogeton pectinatus and Potamogeton pusillus) were well adapted to disturbance tolerance, especially from weed control procedures, but vulnerable to higher saline-stress pressures. Ruppia maritima, Zannichellia palustris and filamentous algae characterised a third group found in shallow, high-salinity, permanently filled channels. All plants of the fourth group ( Potamogeton illinoensis, Elodea callitrichoides, Ceratophyllum demersum, Myriophyllum aquaticum and the floating Azolla filiculoides) are competitive species, which occurred in channels with low environmental stress conditions (low water conductivity and high light availability), but with component species differing in their tolerance of disturbance.